The invention concerns a method of producing color separation images which are essentially orthogonally screened, one for each primary or basic color, suitable for reproduction of an original image, from an original image having at least two primary colors. The separation images so produced appear to have equal screen rulings and each separation image is rotated a certain angle relative to the Y direction. These separation images may be in the form of film negatives or printing plates.
In the art of color reproduction such as by printing, it is common practice to prevent the occurrence of Moire effects in the finished product by using different screen angles relative to a reference direction or pattern for the color separation images produced from an original image, screen ruling of the separation images being equal. The colors used for the separation images generally are yellow, magenta, cyan and black. The different angles with the reference direction or pattern are formed by lines connecting the dots in the several separation images.
It is also known in producing such separation images to scan the original image optically with a constant screen ruling for every primary color and to convert the light intensity of every scanned point to an electric signal which is a function of the color intensity of the scanned point. The electric signal may then be used for directing equipment to produce the respective screened separation images.
Rotation of the separation images to form the different angles may be obtained by rotating the original image to the desired angle for each color or by choosing a different scanning direction for each color. Both methods are complicated.